This invention relates to blends of polycarbonates and polyesters, and sheets and films formed therefrom that may be thermoformed without having to pre-dry the sheets and films.
Polycarbonates are widely used in a variety of molding and extrusion applications. Films or sheets formed from the polycarbonates must be dried prior to thermoforming. If not pre-dried, thermoformed articles formed from the polycarbonates are characterized by the presence of blisters that are unacceptable from an appearance standpoint. Therefore, it would be desirable to provide a manner of forming thermoformed articles without the necessity of pre-drying the polycarbonate sheets or films.
It is accordingly an object of the present invention to provide novel blends or compositions of polycarbonates and specific copolyesters.
It is a further object of this invention to provide novel films and sheets produced from the novel blends or compositions, which films and sheets are thermoformable without previous drying thereof, and wherein the presence of blisters is avoided.
These and other objects and advantages of the present invention will be apparent to those skilled in the art from the following detailed description and claims.
In accordance with the present invention, it has been found that the above and still further objects are achieved by combining at least one or more polycarbonates and at least one or more specified copolyesters, in specific proportions, to provide a new and novel blend or composition that is useful for many applications. In particular, novel sheets and films produced from the novel blends or compositions may be used for packaging food, clothing, pharmaceutical products, signs and skylights, and the like; and, unexpectedly it has been found that the sheets or films may be thermoformed without a necessity of pre-drying and produce articles free of undesirable blisters.
More particularly, in accordance with the present invention, a blend or composition is provided comprising from about 15 to about 40 weight percent (%) polycarbonate and from about 60 to about 85 weight % copolyester. Any polycarbonate may be used. The specific copolyesters used are based on an acid component comprising terephthalic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, or mixtures thereof containing from 15 to about 35 mol percent (%) isophthalic acid and a glycol component comprising from about 80 to 100 mol % 1,4-cyclohexanedimethanol.
In addition to the novel compositions, the present invention is also directed to films and sheets formed from the novel blends that are thermoformable without pre-drying, to provide articles and profiles free of blisters.
Additionally, the present invention is directed to articles of manufacture incorporating the novel compositions and films of the present invention.
The novel blends or compositions of the present invention comprise at least one, or more, polycarbonates and at least one, or more specified copolyesters. The polycarbonate is present in an amount ranging from about 15 to about 40 weight %, based on the weight of the total blend or composition, and the copolyester is present in an amount ranging from about 60 to about 85 weight %, both based on the weight of the total blend or composition. The polycarbonate is preferably present in an amount of about 20 to 28 weight percent and the copolyester is preferably present in an amount of about 80 to 72 weight percent, based on the weight of the total blend composition.
The polycarbonate component of the blend or composition may be any polycarbonate. The polycarbonates suitable for use in the present invention are well known and are generally commercially available. The polycarbonates may be branched or linear. Suitable polycarbonates are exemplified, but not limited to, those described in U.S. Pat. Nos. 3,028,365; 3,334,154; 3,915,926; 4,897,453; 5,674,928; and 5,681,905, all of which are incorporated herein by reference. The polycarbonates may be prepared by a variety of conventional and well known processes which include transesterification, melt polymerization, interfacial polymerization, and the like. The polycarbonates are generally prepared by reacting a dihydric phenol with a carbonate precursor, such as phosgene. Suitable processes for preparing the polycarbonates of the present invention are described, for example, in U.S. Pat. Nos. 4,018,750; 4,123,436; and 3,153,008. Preferred polycarbonates for use in the present invention are aromatic polycarbonates, with aromatic polycarbonates based on bisphenol-A [2,2-bis(4-hydroxyphenyl) propane], such as are obtained by reacting bisphenol-A with phosgene, being more preferred. Diphenyl carbonate or dibutyl carbonate may be utilized in place of phosgene.
The copolyester component of the of the blend or composition of the present invention is at least one, or more of poly(1,4-cyclohexylenedimethylene terephthalate) (PCT), poly(1,4-cyclohexylenedimethylene naphthalenedicarboxylate) (PCN), poly(1,4-cyclohexylenedimethylene 1,4-cyclohexanedicarboxylate) (PCC) copolyesters, or mixtures thereof, containing 15 to about 35 mol % isophthalic acid with a preferred amount being from 20 to about 30 mol % isophthalic acid. The copolyester comprises an acid component comprising from about 65 to about 85 mol percent of a dicarboxylic acid selected from terephthalic acid, naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid or mixtures thereof; from about 15 to about 35 mol percent isophthalic acid; and from 0 to about 20 mol percent of other dicarboxylic acid units. The copolyester comprises a glycol component of about 80 to 100 mol percent 1,4-cyclohexanedimethanol (CHDM) and from 0 to about 20 mol percent other glycol units. The total dicarboxylic acid units is equal to 100 mol percent, the total glycol units is equal to 100 mol percent and the total polyester units is equal to 200 mol percent.
The CHDM and 1,4-cyclohexanedicarboxylic acid moieties used to prepare the copolyesters can be trans, cis or trans/cis mixtures of isomers. Any of the naphthalenedicarboxylic acid isomers or mixtures of isomers can be used with the 1,4-, 1,5-, 2,6-, and 2,7-isomers being preferred.
The other dicarboxylic acid(s) that can be used herein in amounts of from 0 to about 20 mol percent have from about 4 to about 40 carbon atoms. Exemplary of the other dicarboxylic acids suitable for use herein are sulfoisophthalic, sulfodibenzoic, succinic, glutaric, adipic, sebacic, suberic, dimer, dodecanedioic, and the like, or mixtures thereof.
The other glycol unit(s) that can be used herein in amounts of from 0 to about 20 mol percent contain from about 3 to about 12 carbon atoms. Exemplary of the other glycols suitable for use herein are propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, diethylene glycol, and the like, or mixtures thereof.
With respect to the composition of the copolyester, the glycol component preferably comprises 100 mol percent of 1,4-cyclohexanedimethanol. In another preferred embodiment, the acid component of the copolyester comprises 65 to 85 mol percent terephthalic acid. In a most preferred embodiment, the copolyester composition comprises 100 mol percent 1,4-cyclohexanedimethanol, about 26 mol percent isophthalic acid, and about 74 mol percent terephthalic acid.
The copolyester component of the blends of the present invention preferably have an inherent viscosity (I.V.) of from about 0.5 to about 1.5 dL/g, determined in accordance with ASTM Test Method D2857-70.
The copolyester component of the blends of the present invention may be prepared by processes well known in the art. For example, the copolyester components may be readily prepared by batch or continuous processes. These copolyesters are typically made in melt phase polycondensation reactions. However it is possible to use solid phase build up techniques well known in the art, if desired.
One suitable method includes the step of reacting one or more dicarboxylic acids with one or more glycols at a temperature of about 100xc2x0 C. to about 315xc2x0 C. at a pressure of about 0.1 to 760 mm (millimeter) mercury for a time sufficient to form a polyester. For methods of producing polyesters, reference is made to U.S. Pat. No. 3,772,405, the contents of which are incorporated herein by reference.
Furthermore, the copolyesters of the present invention can be prepared by condensation of the appropriate raw materials using either batch or continuous operations well known in the art. It is possible to use dicarboxylic acids or their corresponding lower alkyl esters such as the methyl esters in the polymerization reactions. When using the methyl esters, it is desirable to use titanium, manganese or zinc based catalysts in the initial ester interchange step and titanium, antimony, germanium, or tin based catalysts for the polycondensation step. A preferred catalyst is based on about 10 to about 100 ppm of titanium and 0 to about 75 ppm manganese. During the buildup phase, it is desirable to add from about 10 to about 90 ppm of a phosphorus-containing compound to serve as a color stabilizer. Typically, a phosphorus-containing additive is added in the form of a phosphate, such as phosphoric acid or an organic phosphate ester. Typically lower amounts of phosphorus inhibitors are employed when using lower amounts of titanium in the catalyst system. Suitable phosphate esters for use in preparing the copolyesters of the invention include, but are not limited to, ethyl acid phosphate, diethyl acid phosphate, arylalkyl phosphates and trialkyl phosphates such as triethyl phosphate and tris-2-ethylhexyl phosphate.
In forming the copolyesters of the invention, colorants, sometimes referred to as toners, may be added to impart a desired neutral hue and/or brightness to the resulting copolyester. A preferred method of including colorants is to use a colorant having thermally stable organic colored compounds having reactive end groups such that the colorant is copolymerized and incorporated into the copolyester to improve the hue of the copolyester. For example, colorants such as dyes possessing reactive hydroxyl or carboxyl groups, including but not limited to, blue and red substituted anthraquinones may be copolymerized into the polymer chain. Suitable colorants and dyes are described in detail in U.S. Pat. Nos. 4,521,556; 4,740,581; 4,749,772; 4,749,773; 4,749,774; 4,950,732; 5,252,699; 5,384,377; 5,372,864; 5,340,910; and 5,681,918, herein incorporated by reference in their entirety. When dyes are used as colorants, they may be added during or after an ester interchange or direct esterification reaction. The total amount of dye is generally about 10 ppm or less. It is also possible to use small amounts of cobalt as a toner material. In such cases, the cobalt serves as both a toner as well as a polymer buildup catalyst.
The blends of the present invention may comprise more than one polycarbonate, and more than one copolyester, if desired.
The polycarbonate/copolyester blends of the present invention can be prepared by any technique known in the art. For example, the blends can be prepared by making pellet blends that are then extruded and pelletized. Alternately, pellets of polycarbonate and copolyester may be fed separately and the melts mixed prior to the extrusion operation to form film, sheeting or profiles. The melt blending and extrusion operations are generally conducted at temperatures ranging from about 425xc2x0 F. (218xc2x0 C.) to about 580xc2x0 F. (304xc2x0 C.).
Alternatively, the polycarbonate and copolyester components may be weighed and placed in a plastic bag. The bag is shaken or tumbled by hand to blend the components. This blend can then be fed to an extruder to produce sheeting or film. This technique is useful for small-scale work. In larger scale work, the polycarbonate and copolyester components may be placed in separate hoppers and then metered into the extruder to provide the appropriate blend composition. Further, the polycarbonate and copolyester components may be melt blended in a melt mixing tank, in a sigma blade mixer or in a single or twin screw extruder followed by pelletization or granulation of the blend. This melt mixed blend may then be extruded into film or sheeting.
Further, the blends of the present invention can be made by methods which include the steps of blending the polycarbonate and copolyester portions of the present invention at a temperature of about 25xc2x0 C. (77xc2x0 F.) to 300xc2x0 C. (572xc2x0 F.) for a time sufficient to form a blend composition. Suitable conventional blending techniques include the melt method and the solution-prepared method. Other suitable blending techniques include dry blending and/or extrusion.
The melt blending method includes blending the polymers at a temperature sufficient to melt the polycarbonate and copolyester portions, and thereafter cooling the blend to a temperature sufficient to produce a blend. The term xe2x80x9cmeltxe2x80x9d as used herein includes, but is not limited to, merely softening the polymers. For melt mixing methods generally known in the polymers art, see Mixing and Compounding of Polymers (I. Manas-Zloczower and Z. Tadmor eds, Carl Hanser Verlag publisher, New York 1994).
The solution-prepared method includes dissolving the appropriate weight/weight ratio of copolyester and polycarbonate in a suitable organic solvent such as methylene chloride, mixing the solution, and separating the blend composition from solution by precipitation of the blend or by evaporation of the solvent. Solution-prepared blending methods are generally known in the polymers art.
The blends of the present invention can also contain antioxidants, conventional flame retardants such as phosphorus or halogen compounds, or fillers such as talc or mica, or reinforcing agents such as glass fiber, or carbon fiber. Additives such as pigments, dyes, stabilizers, plasticizers, nucleating agents, and the like, can also be used in the polyesters, polycarbonates, and blends of the present invention to further modify the properties of the inventive blends.
The blends of the present invention are useful in producing molded articles, fibers, films and sheeting.
The blends of polycarbonate and copolyester of the present invention may be foamed during the extrusion operations using techniques well known in the art. For example, useful foaming techniques are disclosed in U.S. Pat. Nos. 5,399,595; 5,482,977; and 5,654,347.
Blends of polycarbonate and copolyesters of the present invention tend to exhibit a yellow coloration. The yellow coloration can be suppressed by adding a phosphite stabilizer to the blend. The phosphite stabilizer may be added as the polycarbonate and the copolyester are extruded. In a preferred embodiment, there is prepared a masterbatch of a suitable phosphite stabilizer in either of the polymer components of the blend. The masterbatch contains from about 2 to about 20 weight percent (%) of the phosphite stabilizer. One suitable stabilizer is distearyl pentaerythritol diphosphite. The resultant polymer blends will generally contain from about 0.1 to about 0.5 weight % phosphite stabilizer. The extruded objects of this invention have a wide range of commercial uses. For example, films and sheeting are useful for signs, skylights, the packaging of foods, clothing, pharmaceutical products and the like. Extruded sheeting may be used as is or thermoformed to provide packaging for foods, hardware and the like.
In addition to the novel blends or compositions, the present invention is also directed to films and sheeting, formed from the novel blends or compositions, that are thermoformable without the necessity of pre-drying the films and sheets, and wherein the presence of blisters is avoided.
The compositions of the present invention may be fabricated into films or sheeting by any technique known in the art. For example, films may be produced by well known cast film, blown film and extrusion coating techniques, the latter including extrusion onto a substrate. Films produced by melt casting or blowing can be thermally bonded or sealed to a substrate using an adhesive. The ordinary artisan, in possession of the present disclosure, can prepare such films and articles containing such films without undue experimentation.
Additionally, the present invention is directed to articles of manufacture incorporating the novel compositions and novel films or sheeting of the present invention. The articles can be produced utilizing any suitable technique.
The invention will be more readily understood by reference to the following examples. There are, of course, many other forms of this invention which will become obvious to one skilled in the art, once the invention has been fully disclosed, and it will accordingly be recognized that these examples are given for the purpose of illustration only, and are not to be construed as limiting the scope of this invention in any way.